The present invention relates to the drying of moisture laden agricultural commodities, and in particular, to an inlet duct for recirculating grain dryers.
In the processing of agricultural commodities, dryers are used to remove moisture from the produce immediately prior to the storage of the same in a silo, elevator, or similar storage structure. Grains such as wheat, corn, rye, and the like, as well as the other commodities such as rice, milo and alphapha are processed in this fashion. These dryers are typically referred to as "grain dryers", and comprise a reservoir which is shaped to retain a variety of commodities therein, and includes at least one large, porous drying portion in which the grain is retained, and through which hot air is blown. The hot air impinges upon the commodity disposed in the porous drying portion, thereby quickly and completely drying the same, and the air is then exhausted directly into the atmosphere. Such dryers are of a single pass design, and inherently require a large quantity of heating energy to adequately dry the grain.
Recirculating grain dryers have been developed to more efficiently dry agricultural commodities by recovering some of the energy in the hot exhaust air, through recirculating at least a portion of the same. The present invention relates to an improvement in a particular type of recirculating grain dryer, such as that disclosed in U.S. Pat. No. 4,048,727 to Botkins, wherein a separate recirculating blower is mounted in a room portion of the dryer, and during the recirculating mode, draws in preheated exhaust air from both the cooling section of the dryer and a lower part of the drying section. The preheated air is further heated, and then blown back into the drying section of the grain dryer. Because the drying air is preheated during the recirculating mode, less energy is required to bring the drying air up to the required temperature, thereby realizing a substantial savings in heating energy.
Although the above referenced type of recirculating grain dryer reduces the consumption of energy necessary to heat the drying air, it does require an additional blower for recirculation, which can increase both manufacturing costs and operating expenses. Hence, the operation of the recirculating blower must be quite efficient to maintain the overall economy of the grain dryer, and further be of a reliable, yet inexpensive design.
Further, in recirculating grain dryers, the exhaust cooling and heating air which is recirculated in the dryer picks up chaff and other debris from the grain as the air is blown through the porous drying portions of the reservoir. This debris is usually a very dry and flammable type of dust, which is blown throughout the dryer during the recirculating mode. Because the recirculating blower must be mounted in or adjacent to the drying column area in which a high concentration of the dust exists, the hazard of fire and/or explosion is increased. This hazard is particularly prevalent in grain dryers having the recirculating blower mounted in a room portion of the dryer, which communicates with the drying column area, such that the air is drawn into the recirculating blower from the room, and the dust collects in the corners and other areas of the room where the air is relatively stagnant.